text:
How does the Bell V-280 (a tiltrotor) rotate, bank, and fly sideways?
Here is a video of Bell V-280 Valor. Seems like the old definition of airplane's control is no longer hold for this kind of airplane. If you click the link, it will go directly to the part I want to ask. First, it made a yawing, or turning in its vertical axis so it can make direction change when it is being hover. However, this airplane has two rotors, and no tail rotor like in normal helicopter. Second, it made shifting or move to its left side. Third, it made backward (reverse) move, beside, of course, forward move when the rotors being up. How did it work?
Another part of that video is here. How did it make turn/banking when it is being cruise? Is it still follow the "normal" way by controlling its aileron?
Note:
The answer posted here is not answered how does the V-22 Osprey make side moving, which it is one of my question, and it is very important.

It probably works the same way as the Osprey. An explanation for the V-22 Osprey here: https://www.globalsecurity.org/military/systems/aircraft/v-22-flt-cntrl.htm

The yaw would be accomplished by angling one rotor a little forward, and the other a little backwards.
The shifting move to the side is accomplished by generating more thrust on one side. Either by increasing the rotor AOA (collective pitch) or increasing RPM.
You increase the lift, until you have your desired roll angle, then you equalize the lift so you don't accidentally flop over.
Flying backwards is accomplished by angling the rotors back, like the opposite of the "pitch" part of the image below.
The turn/bank while in cruise is achieved by combining these principles, while also using its control surfaces.
The V-tail works as both an elevator and rudder.
From the cruise turn you linked to, it looks like the rotors aren't fully forward.
I would guess that we're flying too slow to use our flaperons fully.
The roll would be a mix of flaperon angle, and rotor collective pitch.
All the while our V-tail would work as an elevator.
(On a side note, a cool thing happens with our yaw when we shift our rotors from up to fully forward.
When we hover, yaw is accomplished as mention earlier. When the rotors are fully forward, If we exclude the V-tails yaw function, yaw would be accomplished by increasing the thrust on one engine compared to the other.
The same way we would roll in hover mode, is now yaw in flying mode.)
Please let me know if i missed something, or if you have clarification questions!

Thanks a lot. You answered my questions completely, with graph too. It helped me a lot to easy understand.


text:
Why doesn't the U.S. Federal Government auction their retired but memorable aircraft?
The U.S. Federal Government has scores of old aircraft waiting for dismantling. Why doesn't it auction some of them? Some people might be very much interested in planes such as the B-52, and would be happy if they get it at some considerable price (though, I have no idea what it may be!) to keep them as a memorabilia. Also, this and this suggest that civilians can purchase and fly military aircraft. So why doesn't the federal government give this a shot?

Source

It would be a challenge to find adequate storage space for your private B-52. Right after WW II, many airplanes were auctioned off at these locations, and some people made a small fortune just from the leftover fuel in them.

There are a few reasons for this.
First off they may not want the public, or more importantly potentially enemy nations obtaining a large quantity (or any quantity for that matter) of military planes. Even old war birds can still do a lot of damage if equipped by a person with intent on doing damage.
Secondly, the boneyard you have pictured serves a few purposes. For one it houses aircraft that have reached their life time limit. To keep an airplane flying it takes not only money but a supply of parts (or the resources to make your own under certain FAA rules). Out of service planes may be tough if not impossible to keep flying for no other reason than you cant get airworthy parts for them.
Thirdly, some of the planes in these bone yards are scrapped (or kept there) for reserve parts for the planes still in service. Again airworthy parts are not as simple to get as going to your local car parts store. There are many more regulations around them. In this case you can pull parts from an airworthy plane (if you know the cycles its been through) and use them to fix another plane.
Lastly, and this is mainly speculation, maybe the government is hidings its back up planes in plane sight...
On the note about buying old war birds, rules have changed over time and its not as easy to get ahold of government property as in days past. Some military equipment that sees its way to the public hands actually left the US as a sale to another country then that country sold it into public trade as well. For what its worth Trade-a-Plane has a whole section just for war birds.

To put stuff into context, It was rumored (so I cannot guarantee the authenticity of this claim) that my university declined an engine to go with their old donated F16 out of security concerns, i.e. that some people and organizations would have become a little too 'interested'.
The fact remains that many countries have any old American aircraft, yet are not (or no longer) 'allies' of the United States. They have a correspondingly difficult time to get hold of parts.
For instance:

Iran has F4, F5, F14s and C130s.
Venezuela has F16s
Pakistan has F16s.

Needless to say, none of these could really be considered 'allies'.
Even a seemingly irrelevant piece of metal (that you say would like to use for furniture or what not else) could have value to somebody who has difficulties or limitations in acquiring spare parts for their jets.

I think Pakistan would be quite upset to hear itself not considered an "ally" of the United States :p The US is the second-largest foreign supplier of military equipment to Pakistan after China.

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text:
Is it possible to drive into Gibraltar Airport's runway?
The runway of Gibraltar Airport crosses an active 4 lane highway

Example Video.
My question is are there any security measures which prevent normal traffic from entering the airport through the runway when the runway is not in use?
How much security risk does such a runway intersecting with a civilian road entail?
Edit: To make the situation more realistic, assume that some very hostile elements are heading towards the airport, and maybe they need only 5 minutes to throw a grenade at an aircraft, or open fire or cause some other similar destruction.
I am specifically looking at how fast would the response of airport security at Gibraltar Airport would be in such a situation, especially given that it's a small airport with only around 15 departures a day. And simply if there are any measures to prevent normal traffic from entering the airport boundary in the first place?

Yes you could. I would expect airport security to come right after you.

Grenade or gunfire are probably even more than you need. If a terrorist didn't care about surviving, I imagine they could just drive a big truck in front through those gates and stop it right in front of the plane, once the plane is going fast enough that it can't stop. I don't know whether the intersection is late enough that the plane could just take off earlier to miss the truck.

Sumburgh airport also has a road crossing it. https://tools.wmflabs.org/geohack/geohack.php?pagename=Sumburgh_Airport&params=59_52_53_N_01_17_38_W_type:airport_region:GB

But you could do this at most any airport.  For instance, at the FBO we tie down at (medium-sized commercial airport), access is controlled by a chain-link gate.  If you didn't care about scratching your vehicle, you could drive through it quite easily.

Your question is written with 4 different questions all mixed in.  The title asks if it is possible to drive "into" the runway. The photo and video you posted obviously shows vehicle and pedestrian traffic "on" the runway. So, the question is self-answered.  Next, you ask what security measures are in place to prevent this traffic from going to the airport. (I assume you mean the aircraft parking area of the airport?).  Next you ask for a quantified "risk level". And, finally, you ask what the response would be to a given threat. I suggest you edit to clarify what you want to know.

@yshavit a truck full driving tilt into the nosewheel of a parked plane would be pretty serious, especially if then ignited (the latter has been done in various vehicle attacks).  To ram the gates you'd need to be at the front, or at least only behind small vehicles you could push aside, so to drive airside and attack a stationary plane would be simpler

It’s apparently not all that difficult to drive onto a US Navy base and crash into an F-18. Neither the navy personnel nor the police stopped them, but they did not survive the encounter with a parked jet.

@Jimmy thanks for pointing out! I feel that the accepted answer has roughly everything that I wanted to know, and thus maybe an edit is not required.

There are no physical restraints to entering the runway when the road is open.
You can see from this video of the crossing that Gibraltar police and the base for the Royal Air Force are present. The runway is owned by the Ministry of Defence. Anyone attempting to drive on the runway will probably be intercepted in seconds, although I am not aware of any reported attempts.
They also have a street sweeper to take care of FOD (foreign object debris).1

There are plans to build a new four-lane diversion road and tunnel section. Construction started in 2008 but it still hasn't been completed as of 2018. The crossing across the runway will be kept for exceptional, specific, or emergency use but pedestrians will still be able to use the crossing.

The tunnel opened this morning: https://en.mercopress.com/2023/03/30/gibraltar-airport-tunnel-opens

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text:
Is this an accurate depiction of the internal shape of a turbofan engine?
This image (so commonly used here that the first image reference for it that pops up in a Google search for "jet engine diagram" points back to ASE!)
From Wikipedia
Shows the housing of the actual "jet" section very tightly packaged around the various sized compressor and turbine stages, leaving a diverging/converging path for the bypass airflow.
It seems to me that it would make more sense for the packaging of the inner jet engine to be a fairly even cylinder so the bypass air flows smoothly around it and out the back of the nacelle as I've attempted to depict with the blue line at the bottom, or a somewhat converging shape as I've depicted with the red line at the top.
Source: personal modification of above mentioned Wiki picture. Don't laugh... I drew that with my thumb-operated trackball.
However, as I've typed this question up and looked at the diagram more, I can see where the converging path around the low-pressure turbine section of the jet would add additional pressure to the bypass air and, therefore, additional energy to the escaping air.
Is this simply an "artist's concept" of a cross-section of a turbofan engine, or is it an accurate depiction of the internals?
Note: I do understand that within the jet section of the engine the shaping needs to be tightly packaged to ensure the jet-internal air flows exactly where it's needed, my question is about the flow of the bypass air only.

When I look at pictures online, it seems like not only do they not have the ducts you suggested in the bottom picture -- but the ducts from the top picture are littered with tubes (example). That seems like it's cause all sorts of turbulence. Do the nacelles that the engines sit in also contain the inner ducts for the bypass?

Strictly speaking, no. It is an artist's concept to help us understand the engine schematics better. A better figure would look some thing like this :

GE-90 Cutaway; image from web.stanford.edu
The blue colored region more or less shows the 'cold flow' region (where the bypass air flows). This graphic is better for two reasons- not only does it show that much of the flow takes place in the cold flow half-ducts, but it also shows that how the pipes and tubes that are all over the place are covered.
The figure you linked in the question doesn't show the cold air flow ducts, for simplification. Also, the shape and size of the bypass duct varies from design to design (though they are similar overall).

Differences between two and three shaft engines; image from 1.bp.blogspot.com
In the above figure, you can see that the though both the similarly shaped bypass ducts converge, their location and length is different. Of course, in the real aircraft, these ducts host the thrust reversers, as explained by @mins elsewhere.

Any idea why the leading edge on the top of the duct extends farther out than the bottom?

@yshavit - that's a great basis for a whole new question!

Looking at this again (4 years later), I notice that the drawing that I posted in my question basically matches the hot section of the drawing in the answer, my red line sorta matches the inner shrouding that separates the cold flow from the jet and all it's unaerodynamic plumbing, and my blue line basically matches the nacelle. Not bad for a rookie! :)

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text:
Why is the pilot in this video retracting the spoilers so shortly after landing?
I watched this video (link with time) and wondered why the pilot has retracted the spoilers so shortly after landing.
Because the runway is wet and it looks like the plane is still quite fast even in slow motion. Wouldn't it be better to have more braking grip?

Lol.  Austrian Airlines with a didgeridoo playing in the background.  Love it.

The pilot doesn't retract the spoilers until the airplane has slowed down considerably, at the speed it's traveling at that point the spoilers would be adding no benefits so there's no point keeping them deployed.

There are just two things: It is a rainy day, so I would go safe and let the spoilers extended long. And: Retracting the spoilers and flaps is part of the "After Landing"-Checklist. So there has to be a reason for that. By the way: He retracted the spoilers a few seconds after disengaging the reverser. This should be around 60 knots. So the speed when he retracted the spoilers was approximately around 40 knots, I think still fast enough.

@NoahFisher: Spoilers are not primary brakes, they destroy lift created by the wings so that brakes can be more efficient, and at the same time they create more drag. At 40 kt, no lift will be created. Here is an aerodynamic brake.

@NoahFisher It's worth adding that in most modern airliners the ground spoilers operation is automatic (assuming they are in "armed" mode): they are automatically deployed on touch down of the main landing gears and auto-retracted once reverse thrust is deactivated (usually between 60 to 80 kts).


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Why must Vr be set so precisely?
Why must VR (Rotation Speed) be set so precisely? I mean why can't they just say:

Rotate the Aircraft at 120 to 150 knots

And then, the pilot thinks:

OK, I have a full plane and half full tanks, I think I will rotate at around 135 knots

And then rotates at around that speed?

Because, as with anything in the world of aviation, safety is the main priority.

@J.Hougaard And what makes the plane safer when you rotate at a specific speed. Thats what I want to know.

The short, simple answer is that the calculated Vr speed gives guarantees.

To prevent tail strike? If Vr is too low, then the angle of attack will need to be higher to create the take-off required lift and the tail will touch the runway. There are many occurrences of such miscalculated Vr (e.g. this one /// or /// this one) resulting in tail strikes.

This answer is written for air transport category aircraft.
Introduction
During take-off there are three operationally significant speeds that ensure a safe take-off:

V1 - the take-off decision speed
VR - the rotation speed
V2 - the take-off safety speed

In addition there are three technically important speeds:

VMU the minimum unstick speed
VMCG the minimum controllable speed on the ground in case of an engine failure
VMCA the minimum controllable speed airborne in case of an engine failure

V1 is the take-off decision speed. Below V1, take-off can aborted safely without overrunning the end of the runway. Above V1 the aircraft is unlikely to be able to stop before the end of the runway so in case of an engine failure it is safer to get airborne. V1 needs to exceed VMCG to ensure the aircraft doesn't veer off the runway when accelerating to take off with a single engine.
VR is the rotation speed. At this speed the aircraft should be rotated and will get airborne soon after. The rotation speed ensures that, in the case of an engine failure, lift-off is possible and
V2 is reached at 35 feet at the latest. At the end of the rotation manoeuvre, the aircraft should be airborne. Otherwise the tail will hit the ground. Therefore, VR will need to exceed VMU.
V2 is the minimum speed that needs to be maintained up to acceleration altitude, in the event of an engine failure after V1. Flight at V2 ensures that the minimum required climb gradient is achieved, and that the aircraft is controllable. V2 speed is always greater than VMCA to ensure the aircraft is controllable in flight if an engine failure should happen.

Answer
What will happen if we just pick a VR that "feels good"?
If VRfeel is lower than VMU, we will end up with a tail strike. Even if the rotation would stop just before the tail strike, the increase in aerodynamic drag (lift is generated) will cause the take-off run to be longer than needed, risking not being able to climb over objects at the end of the runway. In addition, if the aircraft has an engine failure during rotation, it may not be able to reach V2 and could become uncontrollable and crash.
When VRfeel is too high, the aircraft risks exceeding the maximum safe tire speed. There is also a risk of not reaching VRfeel before the end of the runway.

References
Airbus operations briefing note on takeoff and departure operations; understanding takeoff speeds
Boeing article: exceeding tire speed
rating during takeoff

Wow, great answer, can you tell more about the "safe tire speed"?

@NoahFisher see the linked article from Boeing. Basically it is the maximum speed that the tire is rated for.

You say that this was "written for air transport category aircraft". Is there any real significant difference for any category of aircraft? Physics works pretty much the same no matter the class of aircraft, it's just that an F-16 will reach Vr faster than an A320 which will (may?) get there sooner than a C150, right? Also, +1 for "Vrfeel"!

@FreeMan in a C150 we don't have V1, Vr and V2; since the aircraft can easily be stopped unless you're taking off on super short runways. On multi-engine aircrafts there is Vmu. Since C150 is single-engine it doesn't have one.

@FreeMan, both the F-16 and the C150 have only a single engine so the point of discussing single-engine-out performance is becomes rather moot. However for multi engine non transport category aircraft the same story line can be used.

It's all about safety. The main reasons are:
1) Rotating too early will result in, best case scenario, a tailstrike, worst case would be leaving ground effect at too slow an airspeed and just stalling right away.
2) Before every flight, the pilot must determine if there is enough runway length to takeoff in. It goes without saying that there's no point doing this calculation if you're not going to stick to it. Even a bit of extra speed greatly increases the amount of runway used for takeoff, and chews through the stopping distance available if something goes wrong. It will also decrease the climbing angle, reducing obstacle clearance.
3) Tyres have a maximum speed, after which they may burst.
Aviators can't afford to be lackadaisical and rotate whenever they feel like. In fact, absolutely nothing in flying should be done without solid planning beforehand.

It is not as exactly as you may think. The optimal speed may is even higher/lower due to unknown factors (human load weight distribution, exact winds etc...).
But the speed you calculate is, roughly, the optimal speed. There is really no meaning in choosing another one.
Imagine you are pressurizing your cars tires. There is mostly a value written on it which is optimal. Then you go for that value, don't you? Why would you just give away free optimization?
In aviation, this is even more critical, as you never ever just make things unnecessarily worse due to safety reasons. Accidents don't happen due to one bad thing, but due to four, five not quite optimal things (a controller, who is a little tired, a radio which is slightly to noisy, wind which is slightly stronger then expected, slightly more resistance on the runway due to heat... that's how accidents happen)

Why downvotes?!


text:
Which authority regulates airliner design?
To which regulating authority's regulations and standards are large sub-sonic transport aircraft (passenger or cargo) designed? The FAA's, or EASA's, or both?

The safe operations of an aircraft is called airworthiness. It is the standard by which an aircraft is determined fit to fly. Responsibility of airworthiness lies with national aviation regulatory bodies, manufacturers, as well as owners and operators. International standards are dictated by ICAO during the aircraft design process:

The International Civil Aviation Organization sets international
  standards and recommended practices for national authorities to base
  their regulations on

FAA has regulations governing all aviation activities in the US. EASA also has airworthiness regulations.
The answer to your question is:

The aircraft manufacturer makes sure that the aircraft meets existing
  design standards, defines the operating limitations and maintenance
  schedules and provides support and maintenance throughout the
  operational life of the aircraft.

Thank you for the answer. Your link to 'regulations' take me to a regulation that governs maintenance for aircraft below 5700 kg used for non-commercial uses. Does this mean that larger aircraft are not governed by airworthiness regulations from EASA, but rather by ICAO recommended practices? It seems you are placing an emphasis on a difference between 'rules' and 'regulations', is this an accurate assessment?

Good catch. I didn't realize that the Wikipedia article had some missing/confusing information. A quick search about EASA's regulations for airworthiness didn't return anything useful. I will try to find some more information and will update my answer.

@Jonny Not quite. ICAO sets general standards, but does not set regulations or issue type certificates; that's done by national(-ish, for the EU) regulators. ICAO recommendations are to national authorities, but the national authorities actually set the rules. The type certificate is issued by the authority where the manufacturer is based (in general, aviation authorities accept each other's type certificates).

@cpast: Indeed. However the individual authorities usually follow the ICAO recommendations quite closely. FAA probably differs most often.

In the USA, the FAA regulates airworthiness. For transport category aircraft, such as Boeing and Airbus, the regulations are in 14 CFR Part 25.

Thanks. Do you know what the EASA regulation is that governs transport category?

No, sorry I don't

I think it is CS-25 Amendment 10


text:
How would you get certified for the AgustaWestland AW609 as a rotorcraft pilot or without any previous certification?
It seems like AgustaWestland might finally get certification for the AW609 in the next couple of years.  Let's say I buy one to transport people to the offshore oil platforms that I hypothetically own.  I'm going to need pilots with a commercial powered-lift rating or possibly an ATP powered-lift, depending on how the aircraft ends up being certified.  Where am I going to find these pilots?
As far as I can tell, the only people who current have FAA powered-lift ratings either converted military ratings from the V-22 Osprey, or are civilian test pilots who worked on the V-22 or AW609 programs.  I guess I could try to hire these pilots, but I will be competing with every other AW609 operator.
Is there a way for rotorcraft pilots to transition to powered-lift?  Is there any way, currently, for a civilian pilot to go from no ratings to commercial powered-lift without getting non-powered-lift ratings first?

I know nothing about powered-lift aircraft, but according to 14 CFR 61.5 they're a separate category for licensing, like airplane, rotorcraft or glider. It is therefore possible to get a "private pilot powered-lift" certificate without having any flying experience in any other aircraft type. 14 CFR 61.109, 61.129 and 61.163 state the flying requirements for private, commercial and ATP powered-lift ratings respectively and 61.65 has the requirements for a powered-lift instrument rating.
61.109(e)(5) does allow substituting some limited airplane (i.e. fixed-wing) experience for powered-lift time:

(5) 10 hours of solo flight time in an airplane or powered-lift
  consisting of at least—

There are also allowances for using simulator and military experience in lieu of powered-lift flight time, but I couldn't see anything that directly allows rotorcraft experience to count towards powered-lift certification. The fact that powered-lift is a category of its own suggests that the FAA considers them to be significantly different from rotorcraft.
So yes, you could theoretically start from zero and work to get your private, instrument, commercial and/or ATP ratings with flying time in powered-lift aircraft only. If, that is, you can find a powered-lift aircraft and an instructor: an ATP requires 1500 hours of experience and doing them all in powered-lift aircraft may not be practical (61.163 only requires 250 of them to be in a powered-lift aircraft).
In reality, I suspect that any civilian powered-lift pilots who are not ex-military are (or will be) people with extensive rotorcraft and/or fixed-wing experience who then follow a training program provided by the aircraft manufacturer. Your insurance company will probably also have a say in who you hire and what experience they have.
Finding and training those people won't be cheap, but if you're buying up new AW609s then you can probably afford it :-)

Hm, somewhat surprises me that some fixed-wing time counts while no rotor time does. I'd expect the rotorcraft part to be the harder, and therefore more useful, part.

It seems that the FAA "powered lift" category lumps together a wide variety of different craft, most notablly tiltrotors and jump jets. I wonder if the rules were written more with jump jets in mind than tiltrotors.


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Is an aircraft's maximum landing weight really weight, or is it mass?
I'm calculating the lift of a Cessna 172 and I don't understand the numbers given for weight. The maximum landing weight is 2550 pounds which is nearly 1134kg. But does that mean 1134 Newtons (weight) or 1134 kilograms (mass)?
Since weight = mass x gravity, I think the weight of the C172 is in Newtons even though it's written using a unit of mass. Am I correct?

No, but the person specifying weight in pounds could have been more explicit. It is pound-force (as opposed to pounds as a unit of mass), and you convert 1 Newton to 0.2248 pound-force. Somehow the insights of Isaac Newton or Galileo Galilei never found their way into the English language or the imperial system. Use the metric system - it is better.

@PeterKämpf *mutter* The English language copes just fine with the concepts of mass and weight, and the system of units you're referring to is American customary units, not Imperial (the two agree on the pound but have different tons and different liquid measures).

As I understand your question, I believe you to be technically correct. However, remember that U.S. aircraft manufacturers typically publish weight limitations in both pounds and kilograms even though the first is a unit of force and the latter a unit of mass, and use a simple constant to convert between the two. Boeing uses 0.45359237 pounds per kilogram. This is a simplification that is workable because the variation in gravity between the surface of the earth the max altitude of aircraft is negligible for the practical purposes of aircraft weight limitations.

Sorry! I made a mistake in question. To be specific, the C172's maximum landing weight is 2550 pound which is nearly 1134kg. Then, does that 1134 means 1134Newton(weight) or just 1134KG(mass)?

The question has an obvious answer: the mass of the C172 is about 2500 lbs, 1130 kg. This is what is sometime referred as weight in layman terms. If someone asks you your weight, usually you provide your mass for the answer and you don't use Newtons. In aviation MTOW is actually the maximum mass.

@Terry, pound may be a unit of either mass or weight, the later being called force-pound if the distinction matters.

@mins, So you mean the weight is 1130 X 9.8 kgm/s^2 ?

@wonwoo Yes, or about 11085 N (+/- some N depending on where you live). Same thing.

Correct, weight is the force created on a mass by the acceleration of gravity. Force = mass × acceleration, and is expressed in Newtons (N). The weight of a C172 is about 1130 kg × 9.81 m/s² = 11,085 N (or 11,085 kg⋅m/s² if you prefer)

99% of everything involving weight is technically incorrect ! 99% of the time, it's about mass to be correct. That's another lost battle over life. You never ask someone his mass, nor read weight in newtons on a can of beans, and that's because on earth, weight vary depending on altitude while mass remain constant. Using weight instead of mass was a language error from the beginning, not only in english, american, but french, spanish, etc. Too late to change that back.

Hmm... This seems like a situation where the pound unit is actually correct and the kilogram unit is incorrect. It's the force that matters (because that's what the wings and/or landing gear have to counter,) not the mass. A pound is a unit a force. A kilogram is not. However, assuming the aircraft are operated near the surface of Earth, a kilogram is proportional to a force, since the Earth's gravity is a reasonable approximation of constant, for this purpose anyway.

Possible duplicate of What is the difference between dry operating weight and dry operating mass?

Unless you're planning on flying your 172 on Mars (spoiler: it won't work), does it really make an actual difference?

On Planet Earth, 1kg of mass exerts 9.81 Newtons of force (weight).
Because this is true anywhere on planet Earth to within a tiny fraction of a percent, we use kg as a convenient measure of weight, even though pedantically it is a measure of mass.
If you are thinking of landing your C-172 on the Moon, Mars, or some other locale where G is different from 9.81 ms-2, then you'll have to convert kg to Newtons of weight.   Otherwise, you should consider kg a unit of both mass and weight.

Pretty large fractions of a percent, actually. Measured accelerations of gravity on Earth's surface vary between 9.76 and 9.83 N/kg, according to Wikipedia. (Also, the symbol for kilogram is kg, not KG).

9.76 is only found on 22,000 ft. mountains near the equator.  And even that differs from 1G (9.81) by approx 0.5%.

Landing a C172 on the Moon, or Mars will be difficult, as flying requires lift which requires a fluid to fly into.

You think lack of a fluid is the most significant problem there??  I think you've got several dozen insurmountable obstacles before fluid-dynamics even enters into the picture/

"One half" is not a "tiny fraction" in my world ...

The fluid density is sometimes the only problem: Beagle descent possibly too fast.

The maximum landing weight given here is actually the mass, not weight.
In general, the various 'weights' given for aircraft are masses, not weights. i.e. they are in kilograms, not Newtons.
This is simply an extension of our everyday usage. As @mins pointed out, if someone asks your weight, you tell your mass (70 kg or whatever), not the weight itself (~686N).

This is correct - since Gravity is (near enough) constant on/near Earth (~9.81 N/kg), mass can be used in lieu of weight - as long as you specify units to avoid ambiguity, anyway. When non-scientists talk about weight they almost always mean mass.

Actually, the actual limit is weight, because it is about the induced drag needed to generate corresponding amount of lift and the thrust needed to overcome that and those are all forces. However, there is a general habit of quoting mass for weight and on Earth it works fine.

Reiterating the point made by @aeroalias, the "weight" that FAA/manufacturer talks about is really "mass" in the pure physics world. However, in the real world, imagine you have a big enough scale to hang the airplane to. The MTOW or Max Take Off Weight would be the reading on that scale. So, if you are weighing your passengers' baggage, use a reliable scale. You can then use it directly in your weight and balance calculations.
So, don't worry about conversions. Just use the real world "weight" in Kgs or Lbs as the case may be as long you are flying on earth.

The FAA weight is the force of the mass on Earth. Divide the weight by 32 to get the mass in SLUGS.

"in the real world, imagine you have a big enough scale to hang the airplane to", large aircraft are weighted using scales below the wheels actually, see How does a commercial airliner measure its weight/mass?

@user3344003, why, (like mins in another post) are you bringing slugs into the discussion?  No pilot has ever computed their aircraft weight, and then decided to convert the unit of measure to slugs.  What would be the point?  Does the POH display weight limits in slugs?  Why is this even a thing?!!!

Aircraft are weighed on scales. Attempting to measure the mass of a loaded aircraft isn't practical. Clearly, the figure indicates weight.

The other answers state the opposite. Would you happen to know something the others don't?

@Federico, I'm not sure whether you are referring to my two initial postulates or my conclusion. While the plane's mass and acceleration ultimately determine the landing load, in practical applications, the starting figure for calculating landing weight is one directly measured by scales placed under the landing gear.

Everyone says that the figure indicates weight, you are the only one claiming it does not. Moreover, even if direct measure is impractical, there are well established estimation methods.

Jim Perris:  "Clearly, the figure indicates weight."  @Federico:  "...you are the only one claiming it does not."  (indicate weight)  I am missing the miscommunication...


text:
Why would aircraft engines be mounted with "toe out"?
According to Wikipedia, on the Douglas DC-4E...

[...] the four 1,450 hp (1,080 kW) Pratt & Whitney R-2180-A Twin Hornet 14-cylinder radials were all mounted with noticeable toe-out, particularly the outer pair.

(Emphasis added)
Why would the engines be mounted toe-out, instead of straight in line with the direction of flight? Is this practice common today?

The first thought that comes to my mind is a better thrust line in an engine out situation. However, toe-out would be counter productive in such a scenario, I should think. Technical specs seem to show 2.5° and 3° toe-out for the inboard and outboard engines respectively.

I think we posted at the same time!

According to this source

The engines were toed out slightly to improve engine-out handling;
  three tailfins were used to ensure that the aircraft could keep flying
  more or less straight if both engines on one wing went down.

I belive it was done to keep the thrust more equal in the event of an outboard engine loss, i.e. they are inline with the direction of flight when an engine loss occurs. Keep in mind that at the time these planes were designed engine failure was a [very]common thing and the mentality was a bit different than it is now. If a little bit of toe out mounting took a speed toll but made the aircraft far more controlable in the event of an engine loss it was considered worth while.
In modern multi-engine propellor aircraft counter rotating propellors (left side and right side props spin oposite directions) are generally employed to fix this problem and avoid the critical engine issue. I do belive that some single engine aircraft still do employ a slightly canted engine position for this reason.

But why does the toe-out improve such engine out handling?

Puts the thrust line closer to the center of mass

Which way would the engine be canted in a single engine plane to combat asymmetric thrust in an engine-out situation?

Is there any thrust in single engine engine-out situation?

@vasin1987: No, but now the turning tendencies normally present from torque, P-factor, etc. are gone.

@FreeMan: My first R/C model (a Carl Goldberg Eagle 2) called for a bit of right thrust to counter left-turning tendencies, and down thrust because of the high wing. I don't know if full-scale planes do that.

@vasin1987 - kinda my point! :) However, @ Fred Larson - interesting... I, obviously, hadn't thought about that.

Toe-out will provide a small thrust vector in the outboard direction which will help counter the turning tendency into the failed engine.  Depending on the aircraft it can also provide additional airflow over the tail to improve rudder effectiveness.

This is a good answer but could be improved.  Specifically, I think that this is not actually true:  "In modern multi-engine propellor aircraft counter rotating propellors (left side and right side props spin oposite directions) are generally employed". As far as I know. counter-rotating props are the exception to the general rule.  It would be interesting to include a few example of modern a/c w/ counter-rotating props but I think it would improve the answer to alter the sentence to indicate that they are unusual cases.


text:
Does runway 32/33R at Madrid actually have a kink in it?
In this satellite image of Madrid airport (MAD/LEMD)...

Source:Google maps satellite view
Alternate link from maps.google.nl still renders incorrectly for me, but appears fine for others...
...it appears that there is a very noticeable left kink in the landing area of runway 32/33R.
According to what I can interpret from Jeppesen's airport data, there doesn't appear to be any indication of this kink:

Page 50 of Jeppesen hosted by uvairlines.com.
Is that kink actually there, or is it an artifact of Google's processing of  different images? There is obviously something going on, as you can see both RWY32 & RWY33 markings in the image, while Jeppesen clearly identifies it as 33.
If that kink is actually there, what impact does that have on a pilot landing? I believe the touchdown target is the two long, solid bars at the top left of the image, which excludes the kink, however, there is enough rubber to indicate that touchdowns have occurred much closer to the threshold than that.

Interestingly I just followed your link and I see the kink too with the 32/33 makings unlike the clear 32 in DeltaLima's answer.

Glad to know I'm not totally crazy and/or being singled out by Google for mind-control experiments, @Notts90 !  :)

Update: on my phone (iPhone 5s) and PC using IE, if I zoom in enough it re-loads the image and I see the straight image DeltaLima gets, if I zoom out I get the kinked image. On PC with chrome I only get the kinked image. So it would appear google have multiple cached images and depending on your browser and zoom level depends which you see.

Maybe they double runway numbers are to account for the kink. The first part of the runway is 33R and the after the kink is 32. :)

@reirab that's the most reasonable explanation I've heard so far! :D

My guess is you have got images of two image sets, one at least being not accurately geo-referenced.. The new set is copyrighted 2017. It's clear two images overlap. "33" is part of the old set, and is the top image, the bottom image ("32") is from the new set. The set used may vary with zoom level.

@mins I understand the copyright date on Google Maps / Google Earth is always the current year. I think only Google Earth shows the actual date of photography.

Looking at both Google Maps and MapQuest I see no kink on the approach end of 32R.

That looks like the overlap (stitching) between two adjacent satelite images. In cities this is much more visible, because houses "lean" the other way compared to their neighbors.

So... Why the downvotes? There are 3 of them so far?

Yes this runway has a kink - because its the medium difficulty  level.  If you scroll 7 parsecs north by south west you'll see the extra-hard difficulty runway, which has a loop-de-loop in it.

I'm voting to close this question as off-topic because it's about aerial mapping and orthorectifying. It would be better answered on gis.se.

An interesting feature of your question is the apparent double-exposure of runway number in your image. And I suspect it will also account for/explain why you see a kink in an image.
Occasionally, runways change number. The reason for this is basically that runways only have 36 possible designations (1-36) however a runway designated 18 may be orientated anywhere from 175-184 degrees. Usually the actual orientation of the runway is rounded to the nearest 10. hence, a runway pointing at 184 degrees would be designated "Runway 18".
Magnetic variation drifts over the years (eg, 10 years ago Southern UK was +3 degrees, now it is +1). This may make a runway which was once 184 degrees magnetic now 186 degrees and that would require its designation to change from "Runway 18" to "Runway 19".
Now, as for your image, I would guess that Google have taken a grab when it was Runway 32, and (at least partially) again once it had been re-designated (and repainted!) Runway 33. This is backed up with the airport's wikipedia article:

On 20 September 2012, both runways 15/33 were renamed as 14R/32L (the longest) and 14L/32R (the shortest).

The act of stitching images together, and the image processing algorithms in use, mean you get kind of a partial of one image and partial of the other. It is almost certainly not there in real life, and thus has no effect on the pilot's handling around that runway.

Actually, @DeltaLima did mention the runway renumbering in his answer, though he didn't provide a reference.

@FreeMan I felt he made a very passing comment to it, and didnt really address that that was clearly the source of your distorted image. I thought you might like some background as to why runways might change numbers. hence the answer.

Fair enough explanation.

@FreeMan Also the 3 answers you have are "Works on my computer", "Works on my computer" and "Its just the image". Nothing I'd call a "good answer to the question" - with no disrespect to other answerers.

This sort of kink appears very frequently throughout Google satellite photos.

@MichaelHampton yes, they do. And I suspect its because google's algorithm uses magnetic north to orientate the image and that varies over time.

This answer seems to come down to "I guess it's an artifact" without giving a rationale for that view. The question wasn't about the markings, it was about the kink. OP used the markings as a way of explaining the kink, but this answer doesn't add to that.

I downvoted because I think it guesses too much: 1) "Google quite obviously orientates their image using magnetic north", 2) this particular kink was caused by image orientation.

don't take it personally, @Jamiec, somebody downvoted my original question. (Without comment, I might add...)

@FreeMan oh I don't take it personally at all. Everyone is entitled to an opinion.

The kink may be the result of the two images, which are being superimposed here,  may have been taken from a different angle and as the Earth is round, not flat, they do not align perfectly.  Normally this is not noticeable as long straight objects are not that common on maps.

Did you bend your screen?
My google maps is better behaved:

Also note that the 15/33 runways were renumbered to 14/32 in somewhere around 2012 due to change in the magnetic heading.

Interesting. I just realized that the date on the Jeppesen plates I found was 2008 and had it marked as 33. Interestingly, even a Ctrl-F5 (forcing Firefox to refresh the image & not pull it from the cache) is still showing a bend. Though, when I zoom out a bit, it's less of a kink from, say 325° to 321°, but more of a chicane to go around that white circle the to left of the 2nd set of 6 bars. Very interesting, and you'll likely get the check for posting a Google map image vs ROIMason's Bing image - I'll give it a bit to see how many other map images show up. :)

Based on Notts90's comment on my OP, are you using the US version of Google maps, or are you in some other country using a localized version? i.e., can you provide the source link for your image? I wonder if there are different images on different servers...

I am in Germany (.de), using the Dutch (.nl) Google maps.

which, interestingly, still renders incorrectly for me! It looks exactly the same as my maps.google.com link. Oh well, I'll just chalk this up to "one of those things"...

@DeltaLima Better even, I can see the dent in one browser (with Maps lite) but not in the other. So it's not only an image processing artefact, but also a caching one

A lot of Google Maps processing is server-side.  So one browser's Javascript engine may badge differently than another's.

This image from Bing maps shows the same region, but without the kink, so I believe this is an image-processing artifact.
Find it on Bing Maps via this link

Source: Bing Maps

The question is whether the runway is straight, so let's start by finding something handy that is a known straight thing.
Notice that the wear marks on the runway (the darker centerline) also slice to one side with the runway - and the 1st law of motion would suggest that is unlikely. This is why I would bet a lot of money on it being an artifact, and not reality.
[lolz] Of course there could be a frequent sideways wind gust that always happens right there, causing the airplanes to move sideways at the exact place that the runway itself is bent...but then why stop there? Maybe the construction crews were similarly affected by that wind, and that's why they built it crooked in the first place![/lolz]

"Maybe the construction crews were similarly affected by that wind...". Naaah. Sangria.

Maybe that wind moved that part of the runway.  :-)

This is most likely an artifact of the error correction in aerial orthophotography.
Planes performing aerial photography or LiDAR will fly a 'windrow' pattern while photographing the landscape, producing long strips of images.

ESRI image
This raw images are then processed and stitched together to create a composite image and orthorectified.  This process is largely automated, the algorithm using similar points as reference points to stitch the images together.  Similar process here, done manually.  Sometimes the edges don't line up perfectly for various reasons: flight vector correction, different lenses, distortion in a lens, etc.  The computer then when stitching the images together stretches or squeezes the image to fit the edge between two known, good reference points.
It interpolates the image which means that sometimes the edges between the reference points don't line up, therefore producing the weird kink in your runway. These errors are common and often found on linear objects where the break is easily recognised.

Re-reading Jamiec's answer about the runway designation:  This is old photography being stitched with old photography just like the answer suggests; the technique is the same and the artifact would look similar too!

FWIW, the other end of 32/33 is labeled 14L. This means (I believe) it is the left of a pair of runways at heading (as you enter it) 140°. Thus the 32/33 end should be labeled 140+180 = 320°, i.e., 32, and since it's now on the right it would be 32R. I measured the actual heading, taking horizontal on my screen to be true east-west (not necessarily so, depending on the details of Google's geographic projection) and got 323°, also consistent with 32 as the correct number. Finally, the kink occurs where a distinct change in background color happens, as one sees often and which is presumably where two different images were joined. The duplicate numbers are in the overlap region. The 33 is bogus (but where it comes from I can't see at all).

The other answers explain why there is an image of the runway labeled as 33.

No, this is just an image registration artifact.

This answer could be improved by providing either an image showing the runway is straight, or providing more info about why this artifact might be here, as the other answers do.

authors: Bob Jarvis - Слава Україні


text:
Why does this V-22's rotors rotate clockwise and anti-clockwise (the right and the left rotor respectively)?

Picture source:
By seeing the blades, we know the rotation's directions. The right side is clockwise and the left side is anti-clockwise. Both seen from the pilot/rear side. During the cruise, the rotation's direction will be like the red marked circles. With such rotation, the rotors will have P-factors on the outer side of both rotors. Mean, on the outer side the thrust will be bigger than on the inner side near the fuselage as depicted by the red straight line. The longer line indicating the bigger thrust are generated and the shorter line indicating the smaller thrust. Of course all will be fine if all working well. The problem is, if one rotor/propeller get fail then another rotor will create more moment to the center of the Yaw-axis, compared to if the rotors rotate in the opposite direction. By rotate in the opposite direction, the bigger thrusts will be near the fuselage so it will be easier to be handled as the yaw force will be smaller.
Then my question is, why did they design so? Why didn't the P-factor put on the inner side near the fuselage to reduce moment to the yaw-axis if one rotor fails?

Comments are not for extended discussion; this conversation has been moved to chat.

Please check this answer from @mins - upon a single engine failure, both props are still driven by the remaining engine.

A couple of things.
One, I suspect the reason is similar to why the arrangement is also used on the P-38 Lightning airplane from World War II. The counterrotating engines on that airplane originally turned in a direction which provided more favorable asymmetric thrust, but during test flying, they found that the propwash interfered with elevator control resulting, I believe, in the death of a test pilot during one flight.
Having a right engine turning clockwise, and a left engine turning counterclockwise, causes the propwash vortices to move out board and avoid interference with the empennage during forward flight.
The second reason on the Osprey is that both engines are interconnected by a drive shaft that runs span wise between the two engine nacelles.  This is necessary, not only for forward flight in the event of an engine failure, but also in hover/vertical flight, where an engine failure would be far more disastrous if both drivetrains were not interconnected.  I suspect that that transverse driveshaft provides an equivalent level of safety to prevent an accident both in hover and  in forward flight.

What is the meaning of the propwash vortices to move out board in this sentence: Having a right engine turning clockwise, and a left engine turning counterclockwise, causes the propwash vortices to move out board and avoid interference with the empennage during forward flight.?

This is correct, but even more important, I'm pretty sure that in the Osprey, even in horizontal flight, if a rotor fails the aircraft will crash. It certainly can't land with only one rotor. So there is no need to minimize or worry about P-factor in that scenario.

Is there not also the effect of cancelling out rotational forces, negating the need for a tail rotor? Similar to the Chinook?

@CharlesBretana, one of its feature they offer is the ability to continue cruise (air plane mode) even with only one side propeller only. Indeed, not possible to hover, but for sure it can land safely. One engine can produce 6000kW, compare to the engine used by B737 Max, one engine can produce power until 8000kW. We are talking maximum load.

@AirCraftLover Search up the flying pancake. High pressure beneath the wing makes it want to spiral up around the tip onto the top of the wing. A tip mounted propeller swirling air the opposite direction alleviates this and increases efficiency. It effectively makes the wing longer.

@AirCraftLover Can you cite a source that an Osprey can fly with one propellor failed?  It can land (not hover) with one engine out, and the other engine driving both rotors.  But it is impossible for me to imagine an Osprey flying in any configuration with one propellor inoperative.  The Osprey's thrust is twice the distance from the centerline of a typical 2-engine airliner, has a much shorter fuselage, and much smaller rudders.

@SnakeDoc You are quite correct.  Without a tail rotor or thrust vectoring, the vertical flight regime would be impossible if the rotors did not counter-rotate.

Everyone here needs to consider what a "propeller failure" even means. There is also some terminology peculiar to V-22 which is missing here, and which suggests that none of the commenters are actually osprey experts.

@DKNguyen, seems like it is the most possible answer of all possibilities. As the propeller located on the tip of the wing, the downwash will definitely created larger spiral force to the wing.

@MaxR, I searched it but I didn't find. It could be mentioned on tv news or mentioned by the related air force staff or by the our DoD or by the so self-claimed expert in aircraft so it not google-able. But for sure, it was mentioned that the V-22 can fly and land safely with one side rotor only. But in my humble opinion, it is very possible as it is a common feature of an airplane can fly with one engine only, even once an airplane in our country still can glide and land on a river with total power loss, just like the airplane land in Hudson river in the US. So, make sense if V-22 also can.

@AirCraftLover Landing with one rotor like an airplane? Or like a helicopter?

@DKNguyen, airplane mode, of course. It is definitely not capable to hover or to land in helicopter mode with only one rotor.

I assume everyone stating that the V-22 can land with only one propellor operating is talking about with both propellors tilted horizontally to the ground, (Helicopter mode), as the tips of the propellor would impact the ground when tilted the other way. And if you mean landing in airplane mode, with no lift from the rotors, that raises the issue as to exactly what the Stall Speed would be for that small wing with no lift being generated by any propellor.

I can't really comment on Carlo's answer about interference with the empennage, but one result of the wingtip propellers turning against the tip vortex is that it effectively increases the length of the wing and aspect ratio, increasing efficiency (in forward flight at least).
One interpretation of this is that it helps reducing the high pressure air under the wing from spilling up and around the edge to the top of the wing. Another is that it reduces the size of the tip vortex. Yet another is that it recaptures the energy in the tip vortex (this is less clear to me though since you have to drive the propeller against the tip vortex which seems like it could mean more work???).
It's not often used because propellers on the wingtips can be structurally difficult, are vulnerable to damage, and this effect works best with very large propellers. But these are things the Osprey already has to live with anyway.
The Flying Pancake took particular advantage of this and my understanding is that it actually relied on the effective increase in aspect ratio to fly (it isn’t going to glide):

Vought V-173 (Wikipedia)

"Experimental and numerical study on wingtip mounted propellers for low aspect ratio UAV design" by Momchil Dimchev

Since the interconnection between motors eliminates the P factor concern, flight efficiency is much better served by inboard up rotation. In horizontal flight the entire wing is placed in the inboard upwash from the ascending propeller blades, getting increased lift essentially free. There is no wing in the outboard downwash as the wing terminates at the engine.

After I compared the V-22 to AW609 and to V-280 with all them are different their empennage form (V-22 is double boom, AW609 is single boom T-shape tail, while the V-280 is V-shape empennage), I then came to conclusion that it is the answer. To make the downwash in outer side will create more lift beneath the wing and beneath the tail. The high T-shape tail of AW609 (reducing effect on the empennage) I think gives more confirmation about it. But however, I think no relation to the interconnection rotor.

An aircraft in flight does not need more lift, though it would benefit from less drag. Can this increased angle of attack (compared to a hypothetical mirror image of the V22) be traded for less drag? Well, at a given speed, weight and g-loading, both aircraft will need to produce the same lift, and if the only influence of rotor direction is on the angle of attack, they will produce the required lift at the same angle of attack - but then the drag of the wing will be the same...

... The drag of the rest of the aircraft may differ due to a difference in pitch, but could that not be compensated for by designing a different angle of incidence of the wing and horizontal stabilizer? To be clear, I suspect there is a wing-rotor interaction making the direction of rotation important, but I feel, from the above, that it is more than a change in the angle of attack - maybe a matter of the lift distribution, or in making the transition between hovering and cruising flight?


text:
What is the reason Light Sport Aircraft (LSA) minimum speed is limited?
I saw an explanation about Icon A5 Light Sport Airplane (LSA), it is said that according to FAA regulation, its stall speed NOT LESS than 45 miles per hour (mph) or around 39.1 knots or around 72 km per hour (kmph). Which is mean, its minimum speed is that 45 mph. I was curious that minimum speed is limited.
Than my question is, what is the reason FAA limits the minimum speed of an airplane? Is that stall speed limitation also applied to another type of airplane?

Photo source:
Edit: Some conversion from mph to knot was not clear. Should be 45mph or 39.1 knots.
Edit 2: I added the minimum speed not less than 45mph.

Your edit is incorrect. The regulation says the stall speed can be no greater than 45kt for an LSA.

Can you provide your source?  Obviously, either Icon got it wrong, or you read it wrong.

I’m voting to close this question because it asks "why is (untrue statement) the rule?"  The entire premise of the question, "stall speed no lower than X" is false.

I am back on the close wagon.  Especially since the OP hasn’t even bothered to enlighten us to the source of the error.  (I searched the Icon A5 website and couldn’t find anything). Perpetuating misinformation benefits nobody.

I’m voting to close this question because it is based on a faulty premise.

The FAA mandates a maximum to the stall speed, not a minimum. The minimum speed must not be higher than a given value.
The minimum speed is limited in order to reduce the risk and severity of accidents, especially during landing. The same was used in FAR 23 where a speed limit of 61 knots was mandated for singe-engined aircraft and multi-engined aircraft of 6000 lbs MTOW or less (§23.49 (6)c).
A slower stall speed translates into a slower approach speed and shorter landing distance. Both help to prevent accidents by giving the pilot more time to get the landing right and come to a stop without crashing. Also, the energy involved is smaller so if something goes wrong the accident is more survivable.

Sorry Peter for my unclear. According to the explanation from the Icon A5, stall speed should not less than 45 mph. Mean, can not be 40mph, but it is alowed to be abouve 45 mph. This is a big question for me, as you said, lower will be saver. That also actually my question, why.

@MichaelHall: Thank you for explaining your downvote.

@Peter Kampf, downvote removed based on your edit.

The FAA’s regulations (14 CFR 1.1, “light sport aircraft”, paragraph 4) require a stall speed no higher than 45kt (51mph) for a plane to be certified as a Light Sport Aircraft. This is a maximum value, not a minimum.
The stall speed is the lowest speed at which the wing generates lift. Below this speed, the plane essentially stops flying and Bad Things(tm) happen, like people dying.
It seems logical that an airplane with a lower stall speed would be safer for sport pilots, who do not need to have as much training as private (or higher) pilots. Flying slower means that things happen in the cockpit at a slower pace, there is more time to correct mistakes and if there is an accident, it will hopefully be less severe.
Ideally, all planes would have a very low stall speed for safety. However, wings designed for higher maximum speeds necessarily have higher stall speeds as well, and that means pilots need more training than a sport pilot gets to be allowed to fly faster planes.

"The stall speed is the minimum speed at which the wing generates lift." This is a bit too much oversimplified. I'm aware you are trying to keep it as simple as possible for this question, but you should at least add that this refers to level flight. A plane can stall at any airspeed and any attitude.

Stall speed is a minimum speed. Mean, the airplane will stop flying if the speed less than that. My question is very clear, the reason: What is the reason FAA limits the minimum speed of an airplane?

@AirCraftLover Not sure what's unclear to you. This answer says exactly why: "lower stall speed would be safer for sport pilots".

@AirCraftLover - As Bianfable has stated, the FAA has mandated built in safety margins into an aircraft with the intention of it being flown by pilots with possibly less time, currency, or proficiency. Poor ADM, IMC, and Stalls/Spins account for a lot of fatalities in GA. LSA regulations limit a lot of the factors which contribute to this. Lower stall speed, less impetus from a lower weight, and a lower passenger capacity help to limit the fatalities for those flying as well as those on the ground.

@Bianfable, the 45 mph is the minimum, not the maximum. Maximum is can be any speed. As I said, FAA limits the minimum speed of an airplane. But why?

@AirCraftLover I know, the FAA limits the maximum value for the stall speed (which by the way is not your minimum speed, you never fly at the stall speed, usually approach speed is 1.3 times the stall speed). And as explained in the answer they limit this because a lower speed means you are safer (accidents are less likely, and less severe).

@MichaelHall This is obviously wrong! Nobody restricts the stall speed to be greater than something. The limit for LSA is that it cannot be larger than 45 knots (51 mph). See e.g. here

@AirCraftLover You are misunderstanding the limit as a minimum, whereas it is actually a maximum.

Thanks for your edit. It helps to explain your misunderstanding. A link to the “explanation about Icon A5” would help even more. Nowhere in the link to your photo source does it mention what you said.
As others have stated, the FAA regulations that define a Light Sport Aircraft specify the maximum stall speed the aircraft must have to be certified. That maximum stall speed is 45 knots indicated airspeed. As a matter of fact, I have flown LSAs with stall speeds of 35 and 31 knots. There is an excerpt from Title 14 Code of Federal Regulations Part 1.1 below.
The confusion lies in the usage of the term “minimum steady flight speed“. If you read the excerpt careful, you may interpret this as a maximum limit as well. The minimum speed at which the aircraft can maintain steady straight and level, unaccelerated flight must be a maximum of 45 knots. It has to be able to maintain steady flight at an airspeed at or below 45 knots. In other words, if the aircraft can not maintain steady flight in the airspeed range between 46 to 120 knots, it can not be certified as an LSA.

Light-sport aircraft means an aircraft, other than a helicopter or powered-lift that, since its original certification, has continued to meet the following:
(1) A maximum takeoff weight of not more than—
(i) 1,320 pounds (600 kilograms) for aircraft not intended for operation on water; or
(ii) 1,430 pounds (650 kilograms) for an aircraft intended for operation on water.
(2) A maximum airspeed in level flight with maximum continuous power (VH) of not more than 120 knots CAS under standard atmospheric conditions at sea level.
(3) A maximum never-exceed speed (VNE) of not more than 120 knots CAS for a glider.
(4) A maximum stalling speed or minimum steady flight speed without the use of lift-enhancing devices (VS1) of not more than 45 knots CAS at the aircraft’s maximum certificated takeoff weight and most critical center of gravity.
(5) A maximum seating capacity of no more than two persons, including the pilot.
(6) A single, reciprocating engine, if powered.
(7) A fixed or ground-adjustable propeller if a powered aircraft other than a powered glider.
(8) A fixed or feathering propeller system if a powered glider.
(9) A fixed-pitch, semi-rigid, teetering, two-blade rotor system, if a gyroplane.
(10) A nonpressurized cabin, if equipped with a cabin.
(11) Fixed landing gear, except for an aircraft intended for operation on water or a glider.
(12) Fixed or retractable landing gear, or a hull, for an aircraft intended for operation on water.
(13) Fixed or retractable landing gear for a glider.


text:
What should you do when ATC gives you a number to call to discuss a violation?
Generally speaking, for those that either have experience calling the number, or, preferably, for those that were paid to answer the phone, what are the benefits or pitfalls of calling?
I had a friend that climbed above his assigned altitude once and was given the number, and he called and had an exceptionally friendly chat, and that was that.
Are there any scenarios, such as gross violations, where it might be better to seek legal counsel first before calling, or not calling at all--especially if there is a discrepancy between airman and controller?

Related: What is a counseling session with the FSDO/FAA? - which is about as far as "the dreaded phone number" usually goes unless you were doing something willfully stupid/dangerous.

Any time you have an accident or cause an incident it never hurts to call AOPA legal (assuming you are a member) to get their advice.

AOPA has an article on exactly this question (written by an attorney). Their advice is basically that it's a judgement call on your part and one that you should think about carefully. Not calling may antagonize the FAA, but calling if it's a major safety issue may be unwise:

That doesn't necessarily mean, however, that you should call the
  telephone number or respond to the FAA's letter, and blather the most
  expansive defense you can conjure up. A little judgment is called for
  here--and, unfortunately, there are no hard and fast rules. If you
  think the FAA may be inclined to just admonish you orally or content
  itself with administrative action, then a humble, cooperative approach
  may be best. Saying you won't talk without a lawyer, when the likely
  outcome if you do talk is minor, may only prompt the FAA to propose
  sterner action. Before you talk, however, think carefully about what
  you want to say, how much to say, what questions the FAA is likely to
  ask and how you'll answer them.
If, on the other hand, there is a substantial chance the FAA will take
  certificate action against you or will propose a fine, the best course
  of action, as I said above, is to hire an attorney. Don't ignore the
  FAA; be polite, but don't provide more information than the bare
  outlines of what is already known and obvious to all. State quietly
  that you understand the FAA's desire to investigate possible
  violations, that you take your obligations to fly safely very
  seriously, and that you will be happy to cooperate. Also say that,
  unless the FAA is not contemplating action against you, you feel it
  best to consult a lawyer before proceeding. Since the FAA likely won't
  give you any guarantees, its representative will be the one
  overreaching if he presses you to respond anyway. Politely decline if
  he does.

I also had a look through the AOPA discussion forums (members only, so no links) and my summary of their comments would be:

File a NASA ASRS form within the 10-day limit, whatever happened
If you know what you did wrong and you know it was minor, then make the call
If you don't know what you did wrong then call but be prepared to end the conversation immediately if you have no good response or you realize it's more serious than you thought
If you know you caused a major safety issue (actual or potential) then don't call and get a lawyer instead
If you know the person you have to call  - e.g. if it's the tower controller at your home airport - then you should give more weight to calling
In general, it's better to call and have to cut off the conversation than not to call in the first place
Whatever you say, keep it short and factual
When you find out what you did wrong, get some ground and/or flight training from an instructor to address that specific issue and have him endorse it in your logbook; this shows the FAA that you've taken the issue seriously and you've actively taken steps to make sure you won't do it again

Note that you have 10 days to fill out the ASRS form in order to avail yourself of the waiver of penalties (subject to a few caveats) - If you call The Number and find out what you did you can submit an ASRS report based on that to protect yourself.

Another good article from AOPA's Flight Training magazine.

I echo @Pondlife's answer - base your response on the severity, and if in any doubt loop in AOPA legal. If you do nothing else, file a NASA ASRS form; it's not a guarantee but it can do no harm.

As a student pilot 15 years ago, I got The Number during an early solo at Paine Field (KPAE) near Seattle.
I received taxi instructions to 34L at A4, did my runup, and called Tower requesting closed pattern, 34L. I was cleared for takeoff, runway 34R. On the upwind, Tower asked me to switch to 132.95... the west-side Tower frequency. Oops. Then they asked me to write down The Number. I finished my landings, because you gotta get back on the horse, then landed, told my instructor, and we called.
By that time the manager had pulled the tapes and determined that, yes, I missed the runway identifier, but the controller also didn't catch that I said I was at a 34L intersection. Everybody was both at fault and not really at fault. Apparently another plane on long final went around, but it wasn't anything crazy dangerous.
All that resulted from the incident was, about two weeks later, the appearance of signs reading "TOWER 132.95" and "TOWER 120.2" at the appropriate intersections. They're still there today! :)

An excellent example of how working through honest mistakes leads to safety improvements for everyone.

From an article in Flying magazine by an aviation lawyer: (quoting from memory, the issue was pre-internet):

In many cases the FAA cannot take any action against you without your
  co-operation. So don't give them any. For example, you are required to
  show (not surrender) your license to an inspector upon request. He
  doesn't get to touch it. And if you are asked "was that your 182
  flying down the beach last Saturday?" your cause is best served by
  silence. Will that make them happy? No. But which would you rather
  have? An angry FAA official who cannot suspend your license, or a very
  happy one who can?

Regarding the "number to call":

Once you have left the aircraft movement area you are no longer air
  traffic and therefore no longer bound to follow their instructions.

He also had this to say about the NASA Air Safety Reporting System:

It is not a coupon good for one free buzz job.
Keep several in your flight bag. Fill them out. Keep the receipt - it has powers similar to a cross on a vampire.
Be concise to a fault. "Landed short" will cover Asiana 214.

In many cases the FAA cannot take any action against you without your co-operation. So don't give them any. <-- I'm sorry but this statement is patently false, and terrible advice: You can't avoid an FAA action by simply pouting silently. If you "don't give them any [cooperation]" the FAA will proceed with whatever action they feel is warranted (up to and including suspension or revocation of your certificates) without the benefit of your input or mitigating circumstances.

Obviously they will proceed with whatever action they have evidence for.  The article says don't give them evidence they don't already have.  If the FAA calls you because somebody got your tail number and complained that you were flying low, don't tearfully admit to doing a buzz-job on your friends BBQ.  Shut your mouth and make them prove it.

Anything you say to the FAA can hurt your case, whether you confess guilt or not. Whether what you say provides evidence the FAA did not yet have, or is something the FAA already knows to be true, even information that shows mitigating circumstances or is exculpatory can be used against you. And if you're absolutely certain you have done nothing wrong, co-operation can still be risky, even though you could not possibly imagine why. Voretaq7's addendum is plausible, but wrong and dangerous advice. If you're ever in this situation, don't let me convince you; this is what you need a lawyer for.

paul, Brian, @MarcksThomas - are you speaking from experience, or is this just hearsay or conventional wisdom? It's great to play hangar lawyer, and I can't necessarily disagree here, but you are stating what sounds like opinion as if it was fact, and that's not helpful unless clearly labeled.

@voretaq7 : some finer points of English: "In many cases" is not fully inclusive. If they have video of you being bad, they will use it. If they think it was you, and need your confirmation/confession, you are not obliged to provide it.

@paul My larger point is the "many" cases you can ignore the phone number (or more seriously a Letter of Investigation) are vanishingly few, and doing so predisposes the FAA (at least my local FSDO) to violation rather than counseling or other options. Remember a pilot can be linked to a flight in many ways: If you filed a flight plan or got a weather briefing with your tail number they'll use that. If you rented the aircraft they're going to the FBO, who will probably give you up. If you got out of the plane & paid the fuel guy they might remember you. etc.)

I would tend to agree with paul's answer and be wary of Pondlife's answer.
In most cases it is mistake to call them, because you are just providing them rope to hang you. If they have actionable evidence to revoke your license, calling them and confirming the information they have will just make it worse. If they do not have actionable evidence and are on a fishing expedition, then obviously it would be a blunder to call them. Basically the likely scenarios are all ones in which calling them is a mistake.
The only exception is when there is some fact which exonerates you completely that they do not know about it. Technically, you are better off presenting such a fact at a hearing, but in the interest of saving everyone's time and trouble, you may opt to reveal such a fact in the phone call. For example: "I descended out of my asssigned altitude because I had an engine failure."
In all honesty, the scenarios in which the call is useful are really rare, and as a rule you should NEVER volunteer information regarding your actions in flight. Note that the worst the FAA can do is revoke your license, but another pilot could sue you for $5 million for "endangering his life". Guess where he will get the evidence to sue you. From your statements to the FAA. Starting to see why it is a bad idea to be making statements to the FAA?

Has this happened to you? Can you cite examples? It's pretty common for pilots to portray the FAA as the bogeyman, so it's nice to know when there's truth to the rumors.

@egid Luckily, I have never in any way violated FAA regulations while flying an aircraft, however, in the few instances in which I have had dealings with FAA (such as with their medical doctors) I have found them to be complete hard asses who exploit their bureaucratic powers to the maximum. If you read the AOPA legal column you can find one horror story after another that will reinforce the importance of following my advice.

I've had the opposite, oddly enough. The Renton FSDO is great, but I've dealt mostly with CFI renewals and the like. Fwiw I don't consider medical examiners FAA - they're ICs.

@egid The people in Oklahoma City are a completely different kettle of fish than the local offices. I have definitely had good experiences with them, but then again I was not being investigated for a violation. Let me put this way: I would not want to get on their bad side.

@egid Also, regardless of how "nice" the FAA is, you are creating a public record when you talk to them, and an injured party, the police or the FBI can also use that legal record against you in a court of law. So, even if the FAA loves you, just creating that legal record puts you at all kinds of risk. For example, if you are in an accident that involves a fatality, you can sued and prosecuted even though you are completely "innocent". You don't want to make it easier for them to do that.

That's true. Still, the severity of the situation has a lot to do with it, and FAA certificate actions have dropped significantly over the last couple decades. I'm not saying the FAA is your friend, but if they're out to get you, there is a fair chance you really screwed up.


text:
What can I do to prepare for private pilot training? (India)
I am an aviation enthusiast from India. I am 24 now and want to be a hobby pilot after 1 or 2 years (I need to save money to afford training).  I want to move up to twin engine aircraft as well.
Since I have fair amount of free time and can understand the concepts clearly with no time pressure, what should I start doing now that will help me tremendously when I train to be a pilot (reading books or doing any other stuff)?  What should be my plan of action?

Welcome to the site! This may be a difficult question to answer clearly because a lot depends on where you are (local regulations and requirements etc.) and even on how you personally like to learn. Are you planning to learn to fly in India? Also, if you prefer or need to discuss this topic in general then you may find the chatroom is a useful alternative to asking a question.

I am planning to learn flying in India, I need a general/specific suggestions on what to read and how to prepare well ahead to actually start training. As I have heard there are many subjects one has to understand and master before becoming a pilot.

It's hard to give you specific advice for India because I'm not familiar with the regulations and standards there (your best bet would be to give the DGCA a call and ask if they have any publications you can review).
Broadly speaking all countries are going to expect you to know much of the same material however (because all airplanes essentially fly the same way). Along those lines, the FAA publishes some of the best flight training resources out there, and it's all available online for free.
I would recommend two of the publications to anyone considering flight training:

The Airplane Flying Handbook
This is where I'd generally suggest starting - a basic "How does all this flying stuff work?" textbook on a par with any of the commercially-produced materials.
Details on specific regulations, procedures, how to read charts, etc. may vary, but all of the material on aerodynamics, systems, flight controls, and maneuvers will be applicable.
If you're interested in helicopters there's a Helicopter Flying Handbook as well.

The Aeronautical Information Manual (direct PDF link)
This will be less useful to you as it's written with US regulations in mind (and stuff like aeronautical charting is probably different in India than it is in the US), but again there are large sections that are broadly applicable: Chapters 1, 2, and 8 in particular.

In addition to reading you can gain some experience using simulators if you use them effectively - even relatively inexpensive home simulation software & equipment can be helpful, though it's not a substitute for the real thing. We've got a good Q&A on using simulators to help in training which addresses some of the strengths and weaknesses of learning in a simulator. To help keep you from developing bad habits you would have to un-learn in a real airplane there are also companies providing what's effectively a private pilot flight course via simulators for free, and that will help you get started doing things right - following all the procedures as you would for a real airplane.

Thanks voretaq7 for the answer. I will contact dgca for further details pertaining to Indian training procedures. The books you referred will really help me a lot.

The AIM link seems to be broken (can't imagine that after 2 years). I've updated it to what I believe to be the correct link now. You may want to double check it.

@FreeMan Right link - The DOT made the FAA take down the HTML version of the AIM. I thought I updated all the links to it so they point to the PDF but I guess I missed this one.


text:
What is the approximate accuracy of ASDE-X?
Can anyone suggest some ballpark figures for estimating the tracking accuracy of ASDE-X systems at airports? Specifically, I'm trying to get a sense of the error (± x meters) that can be expected from ASDE-X when fixing the position of an aircraft.

Are you asking how accurately ASDE-X can fix the position of a single aircraft? And what's the relevance of PDARS (it's a data analysis system)?

@Pondlife.  Sorry I should have been clearer.  The way you phrased it is correct.  Specifically, I'm trying to get a sense of the error (± x meters) that can be expected from ASDE-X when fixing the position of an aircraft.  PDARS is not relevant, I just usually have found the two referenced together which is why I did so.  I hope that helps.  Thanks!

No problem, I edited your question with some information from your comment; you can edit it again yourself if my changes aren't useful, of course.

@Pondlife Thanks, I appreciate it!

The FAA has a bunch of information on ASDE-X, most of which I personally have no idea how to interpret correctly. The ASDE-X procurement specification in particular has a lot of technical details on radar performance and although I didn't understand much of it I did notice this requirement:

3.6.3   Map Registration
The display of target data shall [R306] be registered to the display map with an accuracy of at least 20 feet.

So whatever the technical capabilities of the system are, operationally it seems that you can assume it's accurate to within 20ft, which seems to be reasonable in the context of large aircraft. You may be able to get more out of the documentation than I could, of course.


text:
What is 'level' to a G1000?
I used to fly a Cessna 550 with 'steam gage' mechanical gyros. The Attitude Indicator always had its flight director solidly on the horizon in level flight -- to the extent a mechanical instrument could be seen accurately.
I recently started flying a Phenom 300 with a G1000 panel. It is curious to me that level flight in the Phenom is always about 2.0º nose up pitch:

And a detailed pic of the command bars in level flight at FL430:

My question: Why would level flight be indicated by nose up pitch? What does 'level' actually refer to?

BARO minimums 10,640? Impressive ;)

You are assuming this is due to a difference between the avionics suites, where in reality the difference can be due to aircraft design

This annoys me too.  I have only flown this kind of stuff once or twice, but I don't need the attitude indicator to remind me that some positive AoA is required for lift.  Instead, when I am in instrument conditions I want to set the pitch bug for my zero VSI attitude.

BARO minimums 10,640? Set up for the KTEX RNAV (GPS) Z RWY 9 have a look

Level flight just means not climbing or descending.  Where the nose is actually pointing is another matter.
The pitch you are seeing is the "deck angle".  Pitch attitude is normally referenced to the longitudinal axis of the fuselage (and normally, the cabin floor or deck) relative to the horizon for the loading and speed you are at.
The deck angle will be the overall AOA of the wing for a given flight condition plus or minus the wing incidence relative to the fuselage. If the incidence is zero, meaning the wing mean chord line is parallel to the fuselage's long axis, and the wing is operating at a 2 degree overall AOA at that altitude and speed, there's your pitch attitude; +2.  I would expect to see at least a deck angle of a couple degrees when flying at 210 kt indicated in a jet, unless the wing had an incidence of several degrees.
Say the Phenom has a wing incidence of about 1 degree, and that the wing is actually working at an overall AOA of 3 degrees at 210kt; the resulting deck angle would also be +2.
In the Citation with the mechanical spherical attitude indicator with Flight Director, you have to allow for the parallax error due to the gap between the indicator and sphere if your sight line is off a bit, and perhaps the Citation II has a higher wing incidence, and along with a lower wing loading cruises with a lower deck angle of 1 degree or less. With a mechanical indicator it'd probably look close enough to 0 degrees to make that conclusion.

I was always told that an analog AI should be set to the white horizon line while on level ground, rather than for straight and level flight. The reason for this is that it offers a truer picture of the pitch of the nose above the imaginary horizontal plane.
For example, a Cessna 172 in straight and level flight will actually be in an orientation with the nose about 2.5 degrees above horizontal. It’s entirely likely that the Phenom balances S&L with a slightly nose-up pitch as well. Unfortunately, the G1000 does not offer the ability to calibrate this for yourself according to preference.
Perhaps, take solace in the fact that you now have a somewhat more accurate reading of the actual pitch of the aircraft during its various maneuvers and configurations.

The adjustment on analog gauges is only for parallax, which isn’t an issue with glass.

@StephenS the adjustment is intended to correct for parallax, which is exactly what is does if you adjust it on the ground during run-up. But someone could use it to correct for typical flight attitude and now be disappointed that it isn't available on the glass instrument (which has no parallax to correct for).

At FL430 cruise, your aircraft is probably exhibiting a real nose-up pitch attitude in order to achieve the wing's best-economy AoA at that point in the flight envelope and the electronic detectors in the pitch attitude indication system are showing you this.
Taking a vacuum-driven "steam gauge" gyro apart reveals a set of clever doodads called erector mechanisms inside it which are intended to determine the average direction of "up" on long-term (~tens of minutes) timescales. It is possible, then, that the steam gauge system was nulling out the persistent (but slight) steady-state nose-up pitch condition in high altitude cruise.

near-stall regime of its flight envelope -- Phenom's are not like Lear's; At FL43 or FL45 at normal cruise they are 10 to 15 kts from the barber pole redline (as you can see in the picture) and 50kts above stall speed (which is dynamically calculated, displayed on the speed tape, and not seen in the pic) Throttled back to LRC, we could be cruising at 160 - 170kts indicated and still be 30 kts above stall.

thanks @dawg, will edit. -NN

The erector can nullify slight turn because in a coordinated turn the apparent gravity is still towards the floor. But in an unaccelerated straight and level flight the only inertial force is due to gravity (because there is no acceleration), so it can't null out the steady state pitch that way.

@JanHudec -- I just noticed that error too, before reading your comment.  Funny how that was allowed to stand uncorrected for well over a year.  Likewise flying along in wing-low straight-line slip also wouldn't cause any automatic "correction" of the gyro to make it read incorrectly.

In level flight, it's natural to have some nose-up pitch. You need some angle of attack to produce lift that counteracts gravity. "Level" on the attitude indicator probably refers to 0 angle of attack, or how the plane sits when it's on the ground wheels down and the G1000 is being calibrated.

However, there could be positive angle of attack or, indeed positive wing pitch attitude, of the wing and zero pitch attitude of the airplane (be it the rotor axis or the thrust axis or the seating surface level or whatever.

authors: Vladimir F Героям слава


text:
Does night takeoff and landing currency also count for daytime currency?
My initial thought is that night currency satisfies daytime currency, but what gives me pause is FAR 61.57(a)(2) notes that a non-current pilot is allowed to conduct day VFR or day IFR flights without passengers to obtain currency.  There is no mention of night flight being allowed.  This seems to imply that day flights are required for daytime currency.

If you can do it at night, you can certainly do it during the day.  :-)

Yes, night landings satisfy the requirements of §61.57(a)(1) for both nighttime and daytime currency.
The wording of the regulation is not crystal clear, and some (including me) have thought that the wording of (a)(2) required daytime landings for daytime currency. This is not the case, per the following interpretation from the FAA (Springfield, IL FSDO, dated 16 April 2014):

Please note, in this section, there is no mention of a day or night differences in the regulation.
In 14 CFR 61.57(b) the regulation specifically mentions the requirement for Night Takeoffs and Landings and the time period they can be completed in.   If the passenger carrying will be done at night, the additional requirements of 14 CFR 61.57(b) must be met.
The night takeoffs and landings, as required by 14 CFR 61.57(b), will qualify for both the day and night requirement, provided all other requirements are met.   The day takeoffs and landings will NOT qualify for the night (section (b)) requirement though.
Stanley E. Swank II
  Aviation Safety Inspector
  Springfield, IL FSDO, AGL-19

Other sources on the Internet agree with this interpretation:

Eric Gideon at askacfi.com:

... your three takeoffs and landings to a full stop at night will also fulfill the recent flight experience requirements for day currency.

A thread at pilotsofamerica.com.

The university library has FARs from that far back. I'll check later today and post what i find.

The askacfi post you quote was actually written by me. I stand by that interpretation, and I think that Magnetoz's answer in this topic is the correct interpretation. If there was a limitation on time of day to count for currency, that would've shown up in 61.57(a)(1).

Here's a link to a google books archive of the 1990 FARs, which seems to support Magnetoz's perspective that (a)(2) is explicitly explaining how out-of-currency pilots may become current.

As promised:  http://aviation.stackexchange.com/q/3402/167

So, (a)(2) just specifies one way that the currency may be accomplished (notice the word may instead of must in the wording of the regulation).  (a)(1) specifically says that you must have "at least three takeoffs and three landings within the preceding 90 days" and doesn't specify that they must be during the day.

OK everyone, I have a response from the FSDO and I stand corrected. I have updated the answer accordingly and included the text of the FSDO's response. I'm sorry that my interpretation was wrong and hope no one was misled (though I tried to be fair, up-front and unbiased while I researched this); nevertheless I'm glad I now have a more or less definitive answer!

Yes, night landings count for day currency.
61.57(a)(1) explains:

Except as provided in paragraph (e) of this section, no person may act as a pilot in command of an aircraft carrying passengers or of an aircraft certificated for more than one pilot flight crewmember unless that person has made at least three takeoffs and three landings within the preceding 90 days.

Period.  That's it.
Night currency limitations simply add an extra caveat to the above: you have to have done the landings to a full stop.

But what about 61.57(a)(2)?  It clearly says day VFR or day IFR?
Your question is slightly misleading.  (a)(2) talks about how to regain currency after you've already lost it...and the quote in your question is incorrect.  You said this:

a non-current pilot is allowed to conduct day VFR or day IFR flights without passengers to obtain currency

No!
The reg actually says:

provided no persons or property are carried on board the aircraft, other than those necessary for the conduct of the flight.

A non-current pilot is allowed to act as pilot in command in order to become current, so long as nobody is carried other than those individuals who are necessary for the conduct of the flight.  Such as the first officer, a flight instructor, or an examiner.

So why is there the day limitation?
Because there's no restriction on multi-crew operations at night.
61.57(a)(1)

Except as provided in paragraph (e) of this section, no person may act as a pilot in command of an aircraft carrying passengers or of an aircraft certificated for more than one pilot flight crewmember unless that person has made at least three takeoffs and three landings within the preceding 90 days,

vs
61.57(b)(1)

Except as provided in paragraph (e) of this section, no person may act as pilot in command of an aircraft carrying passengers during the period beginning 1 hour after sunset and ending 1 hour before sunrise, unless within the preceding 90 days that person has made at least three takeoffs and three landings to a full stop during the period beginning 1 hour after sunset and ending 1 hour before sunrise, and

If you need to get current in a multi-crew airplane, you can.  (a)(2) says so.  You don't need to get current in a multi-crew airplane at night, because there's no restriction on multi-crew operations at night.

@dvnrrs - No ambiguity that I can see.  (a)(1) answers the original question.  The rest of it is just confusion about multi-crew operations at night.

Per a response from my local FSDO, this answer (at least the portion stating that night landings count for day currency) is correct. I stand corrected and have updated my own answer below.

Your last sentence is incorrect if you have passengers on board for the flight. You would need to be night current for that because of the fact that you are carrying passengers, whether it is multi-crew or not.

FAR 61.57(a)(2) is for the purpose of fulfilling (a)(1). Meaning, if you are out of day currency than you must make day landings.  If are day current, then night landings will qualify to continue your day currency.

I just passed my PPL checkride a couple of weeks ago, and the examiner asked me this very question.  I said I'd have to look it up in the FAR, but as I started flipping pages he said don't bother... 3 full stop night landings do satisfy the requirements for day currency.


text:
How did the B707 and DC-8 fight stress at the windows?
As it is evident from this  question, 4 (or 3) de Havilland Comets crashed because of stress building around the rectangular windows.
How did DC-8 and B707 fight this problem, especially as it is quite clear that both of them had rectangular windows as well?

No, the Boeing 707 and the DC-8 used radiused corners on all their windows to avoid the problems of stress concentration factors, plus additional pad ups around the openings in the skins for the Windows themselves.

(Source)

authors: Βασίλης Δούκας